Properly check for RX_DROP_UNUSABLE now that the new drop reason
infrastructure is used. Without this change, the comparison will always
be false as a more specific reason is given in the lower bits of result.

Fixes: baa951a1 ("mac80211: use the new drop reasons infrastructure")
Signed-off-by: Benjamin Berg <benjamin.berg@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Link: https://lore.kernel.org/r/20230621120543.412920-2-johannes@sipsolutions.netSigned-off-by: Jakub Kicinski <kuba@kernel.org>